Implantable medical device with pressure sensor

ABSTRACT

An implantable medical device (IMD) is configured with a pressure sensor. The IMD includes a housing and a diaphragm that is exposed to the environment outside of the housing. The diaphragm is configured to transmit a pressure from the environment outside of the housing to a piezoelectric membrane. In response, the piezoelectric membrane generates a voltage and/or a current, which is representative of a pressure change applied to the housing diaphragm. In some cases, only changes in pressure over time are used, not absolute or gauge pressures.

This is a continuation of co-pending U.S. patent application Ser. No.16/104,370, filed Aug. 17, 2018, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/547,458 filed on Aug. 18,2017, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to implantable medical devicesand more particularly to implantable medical devices with pressuresensors

BACKGROUND

Implantable medical devices are commonly used to perform a variety offunctions, such as to monitor one or more conditions and/or deliverytherapy to a patient. In some cases, an implantable medical device maydeliver neuro stimulation therapy to a patient. In some cases, animplantable medical device may simply monitor one or more conditions,such as pressure, acceleration, cardiac events, and may communicate thedetected conditions or events to another device, such as anotherimplantable medical device or an external programmer.

In some cases, an implantable medical device may be configured todeliver pacing and/or defibrillation therapy to a patient. Suchimplantable medical devices may treat patients suffering from variousheart conditions that may result in a reduced ability of the heart todeliver sufficient amounts of blood to a patient's body. In some cases,heart conditions may lead to rapid, irregular, and/or inefficient heartcontractions. To help alleviate some of these conditions, variousdevices (e.g., pacemakers, defibrillators, etc.) may be implanted into apatient's body. When so provided, such devices can monitor and providetherapy, such as electrical stimulation therapy, to the patient's heartto help the heart operate in a more normal, efficient and/or safemanner. In some cases, a patient may have multiple implanted devicesthat cooperate to monitor and/or provide therapy to the patient's heart.

SUMMARY

The present disclosure generally relates to implantable medical devicesand more particularly to implantable medical devices with pressuresensors.

In a first example, a leadless cardiac pacemaker (LCP) may be configuredto sense cardiac activity and to deliver pacing therapy to a patient'sheart. The LCP may comprise a housing having a proximal end and a distalend, a first electrode secured relative to the housing and exposed tothe environment outside of the housing, a second electrode securedrelative to the housing and exposed to the environment outside of thehousing, a diaphragm that is exposed to the environment outside of thehousing, the diaphragm is responsive to an external pressure applied tothe diaphragm by the environment outside of the housing, a piezoelectricmembrane having a first pressure sensor electrode and a second pressuresensor electrode, the piezoelectric membrane may be configured togenerate an electrical voltage between the first pressure sensorelectrode and the second pressure sensor electrode in response to apressure change applied to the diaphragm, the electrical voltagerepresentative of a change in external pressure applied to thediaphragm, and circuitry in the housing operatively coupled to the firstelectrode and the second electrode of the LCP, and also operativelycoupled to the first pressure sensor electrode and the second pressuresensor electrode, the circuitry may be configured to deliver a pacingtherapy to the patient's heart via the first electrode and the secondelectrode of the LCP, wherein the pacing therapy is dependent, at leastin part, on the electrical voltage generated by the piezoelectricmembrane and that is representative of the change in external pressureapplied to the diaphragm.

Alternatively or additionally to any of the examples above, in anotherexample, the circuitry may be configured to detect a pressure pulse bymonitoring the electrical voltage generated between the first pressuresensor electrode and the second pressure sensor electrode by thepiezoelectric membrane.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may have an interior surface that faces toward aninterior of the housing, and the piezoelectric may be secured to atleast part of the interior surface of the diaphragm.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may have an interior surface that faces toward aninterior of the housing, and the piezoelectric membrane may be spaced adistance from the interior surface of the diaphragm and may beoperatively coupled to the interior surface of the diaphragm via anincompressible fluid.

Alternatively or additionally to any of the examples above, in anotherexample, the incompressible fluid may be in a fluid cavity that is atleast partially defined by the interior surface of the diaphragm and maybe in fluid communication with both the interior surface of thediaphragm and the piezoelectric membrane, wherein the fluid cavity maybe configured to communicate a pressure applied to the incompressiblefluid by the diaphragm to the piezoelectric membrane.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may have an interior surface that faces toward aninterior of the housing, and the piezoelectric membrane may be spaced adistance from the interior surface of the diaphragm and may beoperatively coupled to the interior surface of the diaphragm via amechanical linkage, wherein the mechanical linkage may be configured totranslate movement of the diaphragm to a pressure applied to thepiezoelectric membrane.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm of the housing may include one or more contours.

Alternatively or additionally to any of the examples above, in anotherexample, the circuitry may be configured to detect a change in pressurein a first chamber of the heart caused by a contraction of a secondchamber of the heart.

Alternatively or additionally to any of the examples above, in anotherexample, the first chamber may be a ventricle, and the second chambermay be the corresponding atrium.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may be integrally formed with the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may be hermetically sealed to the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the LCP may further comprise a fixation member at the distalend of the housing for fixing the distal end of the housing to animplant site, and wherein the diaphragm of the housing is adjacent theproximal end of the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the housing may include an elongated body with a distal endsurface facing distally and a proximal end surface facing proximally,wherein the diaphragm of the housing may be situated on the proximal endsurface of the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm and/or piezoelectric membrane may be formed tomaximize the dynamic change of the diaphragm and/or piezoelectricmembrane when implanted.

Alternatively or additionally to any of the examples above, in anotherexample, the LCP may further comprise an anti-thrombogenic coatingdisposed over the diaphragm of the housing.

In another example, a leadless cardiac pacemaker (LCP) may be configuredto sense cardiac activity and to deliver pacing therapy to a patient'sheart. The LCP may comprise a housing having a proximal end and a distalend, a first electrode secured relative to the housing and exposed tothe environment outside of the housing, a second electrode securedrelative to the housing and exposed to the environment outside of thehousing, a diaphragm that is exposed to the environment outside of thehousing, the diaphragm is responsive to an external pressure applied tothe diaphragm by the environment outside of the housing, a piezoelectricmembrane having a first pressure sensor electrode and a second pressuresensor electrode, the piezoelectric membrane may be configured togenerate an electrical voltage between the first pressure sensorelectrode and the second pressure sensor electrode in response to apressure change applied to the diaphragm, the electrical voltagerepresentative of a change in external pressure applied to thediaphragm, and circuitry in the housing operatively coupled to the firstelectrode and the second electrode of the LCP, and also operativelycoupled to the first pressure sensor electrode and the second pressuresensor electrode, the circuitry may be configured to deliver a pacingtherapy to the patient's heart via the first electrode and the secondelectrode of the LCP, wherein the pacing therapy is dependent, at leastin part, on the electrical voltage generated by the piezoelectricmembrane and that is representative of the change in external pressureapplied to the diaphragm.

Alternatively or additionally to any of the examples above, in anotherexample, the circuitry may be configured to detect a pressure pulse bymonitoring the electrical voltage generated between the first pressuresensor electrode and the second pressure sensor electrode by thepiezoelectric membrane.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may have an interior surface that faces toward aninterior of the housing, and the piezoelectric membrane may be securedto at least part of the interior surface of the diaphragm.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may have an interior surface that faces toward aninterior of the housing, and the piezoelectric membrane may be spaced adistance from the interior surface of the diaphragm and may beoperatively coupled to the interior surface of the diaphragm via anincompressible fluid.

Alternatively or additionally to any of the examples above, in anotherexample, the incompressible fluid may be in a fluid cavity that is atleast partially defined by the interior surface of the diaphragm and maybe in fluid communication with both the interior surface of thediaphragm and the piezoelectric membrane, wherein the fluid cavity maybe configured to communicate a pressure applied to the incompressiblefluid by the diaphragm to the piezoelectric membrane.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may have an interior surface that faces toward aninterior of the housing, and the piezoelectric membrane may be spaced adistance from the interior surface of the diaphragm and may beoperatively coupled to the interior surface of the diaphragm via amechanical linkage, wherein the mechanical linkage may be configured totranslate movement of the diaphragm to a pressure applied to thepiezoelectric membrane.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm of the housing may include one or more contours.

Alternatively or additionally to any of the examples above, in anotherexample, the circuitry may be configured to detect a change in pressurein a first chamber of the heart caused by a contraction of a secondchamber of the heart.

Alternatively or additionally to any of the examples above, in anotherexample, the first chamber may be a ventricle, and the second chambermay be the corresponding atrium.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may be integrally formed with the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm may be hermetically sealed to the housing.Alternatively or additionally to any of the examples above, in anotherexample, the

LCP may further comprise a fixation member at the distal end of thehousing for fixing the distal end of the housing to an implant site, andwherein the diaphragm of the housing may be adjacent the proximal end ofthe housing.

Alternatively or additionally to any of the examples above, in anotherexample, the housing may include an elongated body with a distal endsurface facing distally and a proximal end surface facing proximally,wherein the diaphragm of the housing may be situated on the proximal endsurface of the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the diaphragm and/or piezoelectric membrane may be formed tomaximize the dynamic change of the diaphragm and/or piezoelectricmembrane when implanted.

In another example, a leadless cardiac pacemaker (LCP) may be configuredto sense cardiac activity and to pace a patient's heart. The LCP maycomprise a housing having a proximal end and a distal end, a firstelectrode secured relative to the housing and exposed to the environmentoutside of the housing, a second electrode secured relative to thehousing and exposed to the environment outside of the housing, thehousing having a diaphragm that is exposed to the environment outside ofthe housing, the diaphragm is responsive to a pressure applied to thediaphragm by the environment outside of the housing, a piezoelectricmaterial operatively coupled to the diaphragm of the housing fordetecting a deflection in the diaphragm by generating charge that isrepresentative of the pressure applied to the diaphragm by theenvironment outside of the housing, and circuitry in the housing inoperative communication with the first electrode, the second electrodeand the piezoelectric material, the circuitry may be configured todeliver a pacing therapy to the patient's heart via the first electrodeand the second electrode, wherein the pacing therapy is dependent, atleast in part, on the charge that is generated by the piezoelectricmaterial and that is representative of the pressure applied to thediaphragm by the environment outside of the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the circuitry may be configured to detect a pressure pulse bymonitoring the charge generated by the piezoelectric material.

Alternatively or additionally to any of the examples above, in anotherexample, the circuitry may be configured to detect a change in pressurein a first chamber of the heart caused by a contraction of a secondchamber of the heart.

Alternatively or additionally to any of the examples above, in anotherexample, the first chamber may be a ventricle, and the second chambermay be the corresponding atrium.

In another example, an implantable medical device (IMD) may comprise ahousing having a proximal end and a distal end, a first electrodesecured relative to the housing and exposed to the environment outsideof the housing, a second electrode secured relative to the housing andexposed to the environment outside of the housing, the housing having adiaphragm that is exposed to the environment outside of the housing, thediaphragm is responsive to a pressure applied to the diaphragm by theenvironment outside of the housing, a piezoelectric membrane disposed onan inner surface of the diaphragm, the piezoelectric membrane generatinga charge in response to the pressure applied to the diaphragm by theenvironment outside of the housing, and circuitry in the housing inoperative communication with the first electrode, the second electrodeand the piezoelectric membrane, the circuitry may be configured todeliver an electrostimulation therapy to the patient's heart via thefirst electrode and the second electrode, wherein the therapy isdependent, at least in part, on the charge that is generated by thepiezoelectric membrane and that is representative of the pressureapplied to the diaphragm by the environment outside of the housing.

Alternatively or additionally to any of the examples above, in anotherexample, the piezoelectric membrane may comprise polyvinylidene fluoride(PVDF).

Alternatively or additionally to any of the examples above, in anotherexample, the circuitry may be configured to detect a change in pressurein a first chamber of a heart caused by a contraction of a secondchamber of the heart.

The above summary is not intended to describe each embodiment or everyimplementation of the present disclosure. Advantages and attainments,together with a more complete understanding of the disclosure, willbecome apparent and appreciated by referring to the followingdescription and claims taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing description of various illustrative embodiments in connectionwith the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of an illustrative leadless cardiacpacemaker (LCP) according to one example of the present disclosure;

FIG. 2 is a schematic block diagram of another medical device (MD),which may be used in conjunction with an LCP 100 (FIG. 1) in order todetect and/or treat cardiac arrhythmias and other heart conditions;

FIG. 3 is a schematic diagram of an exemplary medical system thatincludes multiple LCPs and/or other devices in communication with oneanother;

FIG. 4 is a schematic diagram of an exemplary medical system thatincludes an LCP and another medical device, in accordance with yetanother example of the present disclosure;

FIG. 5 is a schematic diagram of an exemplary medical system thatincludes an LCP and another medical device, in accordance with yetanother example of the present disclosure;

FIG. 6 is a side view of an illustrative LCP;

FIG. 7A is a plan view of an example LCP implanted within a heart duringventricular filling;

FIG. 7B is a plan view of an example LCP implanted within a heart duringventricular contraction;

FIG. 8 is a graph showing example pressures and volumes within the heartover time;

FIG. 9 is a schematic cross-sectional view of an illustrative LCP;

FIG. 10 is a schematic cross-sectional view of an illustrative pressuresensor for use with an implantable medical device (IMD) such as an LCP;

FIG. 11 is a schematic cross-sectional view of an illustrative pressuresensor for use with an IMD such as an LCP;

FIG. 12 is a schematic cross-sectional view of a proximal end portion ofanother illustrative LCP;

FIG. 13 is a schematic cross-sectional view of a proximal end portion ofanother illustrative LCP;

FIG. 14 is a schematic cross-sectional view of a proximal end portion ofanother illustrative LCP; and

FIG. 15 is a schematic cross-sectional view of a proximal end of anotherillustrative LCP.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit aspects of thedisclosure to the particular illustrative embodiments described. On thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure.

DESCRIPTION

The following description should be read with reference to the drawingsin which similar elements in different drawings are numbered the same.The description and the drawings, which are not necessarily to scale,depict illustrative embodiments and are not intended to limit the scopeof the disclosure. While the present disclosure is applicable to anysuitable implantable medical device (IMD), the description below usespacemakers and more particularly leadless cardiac pacemakers (LCP) asparticular examples. A normal, healthy heart induces contraction byconducting intrinsically generated electrical signals throughout theheart. These intrinsic signals cause the muscle cells or tissue of theheart to contract. This contraction forces blood out of and into theheart, providing circulation of the blood throughout the rest of thebody. However, many patients suffer from cardiac conditions that affectthis contractility of their hearts. For example, some hearts may developdiseased tissues that no longer generate or conduct intrinsic electricalsignals. In some examples, diseased cardiac tissues conduct electricalsignals at differing rates, thereby causing an unsynchronized andinefficient contraction of the heart. In other examples, a heart mayinitiate intrinsic signals at such a low rate that the heart ratebecomes dangerously low. In still other examples, a heart may generateelectrical signals at an unusually high rate. In some cases such anabnormality can develop into a fibrillation state, where the contractionof the patient's heart chambers are almost completely de-synchronizedand the heart pumps very little to no blood. Implantable medicaldevices, which may be configured to determine occurrences of suchcardiac abnormalities or arrhythmias and deliver one or more types ofelectrical stimulation therapy to patient's hearts, may help toterminate or alleviate these and other cardiac conditions.

FIG. 1 depicts an illustrative leadless cardiac pacemaker (LCP) that maybe implanted into a patient and may operate to prevent, control, orterminate cardiac arrhythmias in patients by, for example, appropriatelyemploying one or more therapies (e.g., anti-tachycardia pacing (ATP)therapy, cardiac resynchronization therapy (CRT), bradycardia therapy,defibrillation pulses, or the like). As can be seen in FIG. 1, the LCP100 may be a compact device with all components housed within the LCP100 or directly on the housing 120. In the example shown in FIG. 1, theLCP 100 may include a communication module 102, a pulse generator module104, an electrical sensing module 106, a mechanical sensing module 108,a processing module 110, a battery 112, and electrodes 114. The LCP 100may include more or less modules, depending on the application.

The communication module 102 may be configured to communicate withdevices such as sensors, other medical devices, and/or the like, thatare located externally to the LCP 100. Such devices may be locatedeither external or internal to the patient's body. Irrespective of thelocation, remote devices (i.e., external to the LCP 100 but notnecessarily external to the patient's body) can communicate with the LCP100 via the communication module 102 to accomplish one or more desiredfunctions. For example, the LCP 100 may communicate information, such assensed electrical signals, data, instructions, messages, etc., to anexternal medical device through the communication module 102. Theexternal medical device may use the communicated signals, data,instructions and/or messages to perform various functions, such asdetermining occurrences of arrhythmias, delivering electricalstimulation therapy, storing received data, analyzing received data,and/or performing any other suitable function. The LCP 100 mayadditionally receive information such as signals, data, instructionsand/or messages from the external medical device through thecommunication module 102, and the LCP 100 may use the received signals,data, instructions and/or messages to perform various functions, such asdetermining occurrences of arrhythmias, delivering electricalstimulation therapy, storing received data, analyzing received data,and/or performing any other suitable function. The communication module102 may be configured to use one or more methods for communicating withremote devices. For example, the communication module 102 maycommunicate via radiofrequency (RF) signals, inductive coupling, opticalsignals, acoustic signals, conducted communication signals, and/or anyother signals suitable for communication.

In the example shown in FIG. 1, the pulse generator module 104 may beelectrically connected to the electrodes 114. In some examples, the LCP100 may include one or more additional electrodes 114′. In suchexamples, the pulse generator 104 may also be electrically connected tothe additional electrodes 114′. The pulse generator module 104 may beconfigured to generate electrical stimulation signals. For example, thepulse generator module 104 may generate electrical stimulation signalsby using energy stored in a battery 112 within the LCP 100 and deliverthe generated electrical stimulation signals via the electrodes 114and/or 114′. Alternatively, or additionally, the pulse generator 104 mayinclude one or more capacitors, and the pulse generator 104 may chargethe one or more capacitors by drawing energy from the battery 112. Thepulse generator 104 may then use the energy of the one or morecapacitors to deliver the generated electrical stimulation signals viathe electrodes 114 and/or 114′. In at least some examples, the pulsegenerator 104 of the LCP 100 may include switching circuitry toselectively connect one or more of the electrodes 114 and/or 114′ to thepulse generator 104 in order to select which of the electrodes 114/114′(and/or other electrodes) the pulse generator 104 delivers theelectrical stimulation therapy. The pulse generator module 104 maygenerate electrical stimulation signals with particular features or inparticular sequences in order to provide one or multiple of a number ofdifferent stimulation therapies. For example, the pulse generator module104 may be configured to generate electrical stimulation signals toprovide electrical stimulation therapy to combat bradycardia,tachycardia, cardiac dyssynchrony, bradycardia arrhythmias, tachycardiaarrhythmias, fibrillation arrhythmias, cardiac synchronizationarrhythmias and/or to produce any other suitable electrical stimulationtherapy. Some more common electrical stimulation therapies includebradycardia therapy, anti-tachycardia pacing (ATP) therapy, cardiacresynchronization therapy (CRT), and cardioversion/defibrillationtherapy.

In some examples, the LCP 100 may not include a pulse generator 104 ormay turn off the pulse generator 104. When so provided, the LCP 100 maybe a diagnostic only device. In such examples, the LCP 100 may notdeliver electrical stimulation therapy to a patient. Rather, the LCP 100may collect data about cardiac electrical activity and/or physiologicalparameters of the patient and communicate such data and/ordeterminations to one or more other medical devices via thecommunication module 102.

In some examples, the LCP 100 may include an electrical sensing module106, and in some cases, a mechanical sensing module 108. The electricalsensing module 106 may be configured to sense the cardiac electricalactivity of the heart. For example, the electrical sensing module 106may be connected to the electrodes 114/114′, and the electrical sensingmodule 106 may be configured to receive cardiac electrical signalsconducted through the electrodes 114/114′. The cardiac electricalsignals may represent local information from the chamber in which theLCP 100 is implanted. For instance, if the LCP 100 is implanted within aventricle of the heart, cardiac electrical signals sensed by the LCP 100through the electrodes 114/114′ may represent ventricular cardiacelectrical signals. The mechanical sensing module 108 may include one ormore sensors, such as an accelerometer, a blood pressure sensor, a heartsound sensor, a blood-oxygen sensor, a temperature sensor, a flow sensorand/or any other suitable sensors that are configured to measure one ormore mechanical and/or chemical parameters of the patient. Both theelectrical sensing module 106 and the mechanical sensing module 108 maybe connected to a processing module 110, which may provide signalsrepresentative of the sensed mechanical parameters. Although describedwith respect to FIG. 1 as separate sensing modules, in some cases, theelectrical sensing module 106 and the mechanical sensing module 108 maybe combined into a single sensing module, as desired.

The electrodes 114/114′ can be secured relative to the housing 120 butexposed to the tissue and/or blood surrounding the LCP 100. In somecases, the electrodes 114 may be generally disposed on either end of theLCP 100 and may be in electrical communication with one or more of themodules 102, 104, 106, 108, and 110. The electrodes 114/114′ may besupported by the housing 120, although in some examples, the electrodes114/114′ may be connected to the housing 120 through short connectingwires such that the electrodes 114/114′ are not directly securedrelative to the housing 120. In examples where the LCP 100 includes oneor more electrodes 114′, the electrodes 114′ may in some cases bedisposed on the sides of the LCP 100, which may increase the number ofelectrodes by which the LCP 100 may sense cardiac electrical activity,deliver electrical stimulation and/or communicate with an externalmedical device. The electrodes 114/114′ can be made up of one or morebiocompatible conductive materials such as various metals or alloys thatare known to be safe for implantation within a human body. In someinstances, the electrodes 114/114′ connected to LCP 100 may have aninsulative portion that electrically isolates the electrodes 114/114′from adjacent electrodes, the housing 120, and/or other parts of the LCP100.

The processing module 110 can be configured to control the operation ofthe LCP 100. For example, the processing module 110 may be configured toreceive electrical signals from the electrical sensing module 106 and/orthe mechanical sensing module 108. Based on the received signals, theprocessing module 110 may determine, for example, occurrences and, insome cases, types of arrhythmias. Based on any determined arrhythmias,the processing module 110 may control the pulse generator module 104 togenerate electrical stimulation in accordance with one or more therapiesto treat the determined arrhythmia(s). The processing module 110 mayfurther receive information from the communication module 102. In someexamples, the processing module 110 may use such received information tohelp determine whether an arrhythmia is occurring, determine a type ofarrhythmia, and/or to take particular action in response to theinformation. The processing module 110 may additionally control thecommunication module 102 to send/receive information to/from otherdevices.

In some examples, the processing module 110 may include a pre-programmedchip, such as a very-large-scale integration (VLSI) chip and/or anapplication specific integrated circuit (ASIC). In such embodiments, thechip may be pre-programmed with control logic in order to control theoperation of the LCP 100. By using a pre-programmed chip, the processingmodule 110 may use less power than other programmable circuits (e.g.,general purpose programmable microprocessors) while still being able tomaintain basic functionality, thereby potentially increasing the batterylife of the LCP 100. In other examples, the processing module 110 mayinclude a programmable microprocessor. Such a programmablemicroprocessor may allow a user to modify the control logic of the LCP100 even after implantation, thereby allowing for greater flexibility ofthe LCP 100 than when using a pre-programmed ASIC. In some examples, theprocessing module 110 may further include a memory, and the processingmodule 110 may store information on and read information from thememory. In other examples, the LCP 100 may include a separate memory(not shown) that is in communication with the processing module 110,such that the processing module 110 may read and write information toand from the separate memory.

The battery 112 may provide power to the LCP 100 for its operations. Insome examples, the battery 112 may be a non-rechargeable lithium-basedbattery. In other examples, a non-rechargeable battery may be made fromother suitable materials, as desired. Because the LCP 100 is animplantable device, access to the LCP 100 may be limited afterimplantation. Accordingly, it is desirable to have sufficient batterycapacity to deliver therapy over a period of treatment such as days,weeks, months, years or even decades. In some instances, the battery 112may a rechargeable battery, which may help increase the useable lifespanof the LCP 100. In still other examples, the battery 112 may be someother type of power source, as desired.

To implant the LCP 100 inside a patient's body, an operator (e.g., aphysician, clinician, etc.), may fix the LCP 100 to the cardiac tissueof the patient's heart. To facilitate fixation, the LCP 100 may includeone or more anchors 116. The anchor 116 may include any one of a numberof fixation or anchoring mechanisms. For example, the anchor 116 mayinclude one or more pins, staples, threads, screws, helix, tines, and/orthe like. In some examples, although not shown, the anchor 116 mayinclude threads on its external surface that may run along at least apartial length of the anchor 116. The threads may provide frictionbetween the cardiac tissue and the anchor to help fix the anchor 116within the cardiac tissue. In other examples, the anchor 116 may includeother structures such as barbs, spikes, or the like to facilitateengagement with the surrounding cardiac tissue.

FIG. 2 depicts an example of another medical device (MD) 200, which maybe used in conjunction with an LCP 100 (FIG. 1) in order to detectand/or treat cardiac arrhythmias and other heart conditions. In theexample shown, the MD 200 may include a communication module 202, apulse generator module 204, an electrical sensing module 206, amechanical sensing module 208, a processing module 210, and a battery218. Each of these modules may be similar to the modules 102, 104, 106,108, and 110 of the LCP 100. Additionally, the battery 218 may besimilar to the battery 112 of the LCP 100. In some examples, the MD 200may have a larger volume within the housing 220 than LCP 100. In suchexamples, the MD 200 may include a larger battery and/or a largerprocessing module 210 capable of handling more complex operations thanthe processing module 110 of the LCP 100.

While it is contemplated that the MD 200 may be another leadless devicesuch as shown in FIG. 1, in some instances the MD 200 may include leadssuch as leads 212. The leads 212 may include electrical wires thatconduct electrical signals between the electrodes 214 and one or moremodules located within the housing 220. In some cases, the leads 212 maybe connected to and extend away from the housing 220 of the MD 200. Insome examples, the leads 212 are implanted on, within, or adjacent to aheart of a patient. The leads 212 may contain one or more electrodes 214positioned at various locations on the leads 212, and in some cases atvarious distances from the housing 220. Some of the leads 212 may onlyinclude a single electrode 214, while other leads 212 may includemultiple electrodes 214. Generally, the electrodes 214 are positioned onthe leads 212 such that when the leads 212 are implanted within thepatient, one or more of the electrodes 214 are positioned to perform adesired function. In some cases, the one or more of the electrodes 214may be in contact with the patient's cardiac tissue. In some cases, theone or more of the electrodes 214 may be positioned substernally orsubcutaneously but adjacent the patient's heart. In some cases, theelectrodes 214 may conduct intrinsically generated electrical signals tothe leads 212, e.g., signals representative of intrinsic cardiacelectrical activity. The leads 212 may, in turn, conduct the receivedelectrical signals to one or more of the modules 202, 204, 206, and 208of the MD 200. In some cases, the MD 200 may generate electricalstimulation signals, and the leads 212 may conduct the generatedelectrical stimulation signals to the electrodes 214. The electrodes 214may then conduct the electrical signals and delivery the signals to thepatient's heart (either directly or indirectly).

The mechanical sensing module 208, as with the mechanical sensing module108, may contain or be electrically connected to one or more sensors,such as accelerometers, blood pressure sensors, heart sound sensors,blood-oxygen sensors, acoustic sensors, ultrasonic sensors and/or othersensors which are configured to measure one or more mechanical/chemicalparameters of the heart and/or patient. In some examples, one or more ofthe sensors may be located on the leads 212, but this is not required.In some examples, one or more of the sensors may be located in thehousing 220.

While not required, in some examples, the MD 200 may be an implantablemedical device. In such examples, the housing 220 of the MD 200 may beimplanted in, for example, a transthoracic region of the patient. Thehousing 220 may generally include any of a number of known materialsthat are safe for implantation in a human body and may, when implanted,hermetically seal the various components of the MD 200 from fluids andtissues of the patient's body.

In some cases, the MD 200 may be an implantable cardiac pacemaker (ICP).In this example, the MD 200 may have one or more leads, for exampleleads 212, which are implanted on or within the patient's heart. The oneor more leads 212 may include one or more electrodes 214 that are incontact with cardiac tissue and/or blood of the patient's heart. The MD200 may be configured to sense intrinsically generated cardiacelectrical signals and determine, for example, one or more cardiacarrhythmias based on analysis of the sensed signals. The MD 200 may beconfigured to deliver CRT, ATP therapy, bradycardia therapy, and/orother therapy types via the leads 212 implanted within the heart or inconcert with the LCP by commanding the LCP to pace. In some examples,the MD 200 may additionally be configured provide defibrillationtherapy.

In some instances, the MD 200 may be an implantablecardioverter-defibrillator (ICD). In such examples, the MD 200 mayinclude one or more leads implanted within a patient's heart. The MD 200may also be configured to sense cardiac electrical signals, determineoccurrences of tachyarrhythmias based on the sensed signals, and may beconfigured to deliver defibrillation therapy in response to determiningan occurrence of a tachyarrhythmia. In some instances, the MD 200 may bea subcutaneous implantable cardioverter-defibrillator (S-ICD). Inexamples where the MD 200 is an S-ICD, one of the leads 212 may be asubcutaneously implanted lead. In at least some examples where the MD200 is an S-ICD, the MD 200 may include only a single lead which isimplanted subcutaneously, but this is not required. In some cases, theS-ICD lead may extend subcutaneously from the S-ICD can, around thesternum and may terminate adjacent the interior surface of the sternum.

In some examples, the MD 200 may not be an implantable medical device.Rather, the MD 200 may be a device external to the patient's body, andmay include skin-electrodes that are placed on a patient's body. In suchexamples, the MD 200 may be able to sense surface electrical signals(e.g., cardiac electrical signals that are generated by the heart orelectrical signals generated by a device implanted within a patient'sbody and conducted through the body to the skin). In such examples, theMD 200 may be configured to deliver various types of electricalstimulation therapy, including, for example, defibrillation therapy. TheMD 200 may be further configured to deliver electrical stimulation viathe LCP by commanding the LCP to deliver the therapy.

FIG. 3 shows an example medical device system with a communicationpathway through which multiple medical devices 302, 304, 306, and/or 310may communicate. In the example shown, the medical device system 300 mayinclude LCPs 302 and 304, an external medical device 306, and othersensors/devices 310. The external device 306 may be any of the devicesdescribed previously with respect to MD 200. In some embodiments, theexternal device 306 may be provided with or be in communication with adisplay 312. The display 312 may be a personal computer, tabletcomputer, smart phone, laptop computer, or other display as desired. Insome instances, the display 312 may include input means for receiving aninput from a user. For example, the display 312 may also include akeyboard, mouse, actuatable (e.g., pushable) buttons, or a touchscreendisplay. These are just examples. The other sensors/devices 310 may beany of the devices described previously with respect to the MD 200. Insome instances, the other sensors/devices 310 may include a sensor, suchas an accelerometer or blood pressure sensor, or the like. In somecases, the other sensors/devices 310 may include an external programmerdevice that may be used to program one or more devices of the system300.

Various devices of the system 300 may communicate via a communicationpathway 308. For example, the LCPs 302 and/or 304 may sense intrinsiccardiac electrical signals and may communicate such signals to one ormore other devices 302/304, 306, and 310 of the system 300 via thecommunication pathway 308. In one example, one or more of the devices302/304 may receive such signals and, based on the received signals,determine an occurrence of an arrhythmia. In some cases, the device ordevices 302/304 may communicate such determinations to one or more otherdevices 306 and 310 of the system 300. In some cases, one or more of thedevices 302/304, 306, and 310 of the system 300 may take action based onthe communicated determination of an arrhythmia, such as by delivering asuitable electrical stimulation to the heart of the patient. In anotherexample, the LCPs 302 and/or 304 may sense indications of blood pressure(e.g., via one or more pressure sensors) and indications of volume(e.g., via an impedance between the electrodes of an LCP or between LCPsvia an ultrasound transducer placed within the LCP, or via strainsensors placed on the heart in communication with the LCP). In oneexample, one or more of the devices 302/304 may receive such signalsand, based on the received signals, determine a pressure-volume loop,and in some cases may communicate such information to one or more otherdevices 302/304, 306, and 310 of the system 300 via the communicationpathway 308.

It is contemplated that the communication pathway 308 may communicateusing RF signals, inductive coupling, conductive coupling opticalsignals, acoustic signals, or any other signals suitable forcommunication. Additionally, in at least some examples, the devicecommunication pathway 308 may comprise multiple signal types. Forinstance, the other sensors/device 310 may communicate with the externaldevice 306 using a first signal type (e.g., RF communication) butcommunicate with the LCPs 302/304 using a second signal type (e.g.,conducted communication, inductive communication). Further, in someexamples, communication between devices may be limited. For instance, asdescribed above, in some examples, the LCPs 302/304 may communicate withthe external device 306 only through the other sensors/devices 310,where the LCPs 302/304 send signals to the other sensors/devices 310,and the other sensors/devices 310 relay the received signals to theexternal device 306.

In some cases, the communication pathway 308 may include conductedcommunication. Accordingly, devices of the system 300 may havecomponents that allow for such conducted communication. For instance,the devices of the system 300 may be configured to transmit conductedcommunication signals (e.g., current and/or voltage pulses) into thepatient's body via one or more electrodes of a transmitting device, andmay receive the conducted communication signals (e.g., pulses) via oneor more electrodes of a receiving device. The patient's body may“conduct” the conducted communication signals (e.g., pulses) from theone or more electrodes of the transmitting device to the electrodes ofthe receiving device in the system 300. In such examples, the deliveredconducted communication signals (e.g., pulses) may differ from pacing orother therapy signals. For example, the devices of the system 300 maydeliver electrical communication pulses at an amplitude/pulse width thatis sub-threshold to the heart. Although, in some cases, theamplitude/pulse width of the delivered electrical communication pulsesmay be above the capture threshold of the heart, but may be deliveredduring a refractory period of the heart and/or may be incorporated in ormodulated onto a pacing pulse, if desired.

Delivered electrical communication pulses may be modulated in anysuitable manner to encode communicated information. In some cases, thecommunication pulses may be pulse width modulated or amplitudemodulated. Alternatively, or in addition, the time between pulses may bemodulated to encode desired information. In some cases, conductedcommunication pulses may be voltage pulses, current pulses, biphasicvoltage pulses, biphasic current pulses, or any other suitableelectrical pulse as desired.

In some cases, the communication pathway 308 may include inductivecommunication, and when so provided, the devices of the system 300 maybe configured to transmit/receive inductive communication signals.

FIGS. 4 and 5 show illustrative medical device systems that may beconfigured to operate according to techniques disclosed herein. In FIG.4, an LCP 402 is shown fixed to the interior of the right ventricle ofthe heart 410, and a pulse generator 406 is shown coupled to a lead 412having one or more electrodes 408 a, 408 b, 408 c. In some cases, thepulse generator 406 may be part of a subcutaneous implantablecardioverter-defibrillator (S-ICD), and the one or more electrodes 408a, 408 b, 408 c may be positioned subcutaneously adjacent the heart. Insome cases, the S-ICD lead may extend subcutaneously from the S-ICD can,around the sternum and one or more electrodes 408 a, 408 b, 408 c may bepositioned adjacent the interior surface of the sternum. In some cases,the LCP 402 may communicate with the subcutaneous implantablecardioverter-defibrillator (S-ICD).

In some cases, the LCP 402 may be in the left ventricle, right atrium orleft atrium of the heart, as desired. In some cases, more than one LCP402 may be implanted. For example, one LCP may be implanted in the rightventricle and another may be implanted in the right atrium. In anotherexample, one LCP may be implanted in the right ventricle and another maybe implanted in the left ventricle. In yet another example, one LCP maybe implanted in each of the chambers of the heart.

In FIG. 5, an LCP 502 is shown fixed to the interior of the leftventricle of the heart 510, and a pulse generator 506 is shown coupledto a lead 512 having one or more electrodes 504 a, 504 b, 504 c. In somecases, the pulse generator 506 may be part of an implantable cardiacpacemaker (ICP) and/or an implantable cardioverter-defibrillator (ICD),and the one or more electrodes 504 a, 504 b, 504 c may be positioned inthe heart 510.

In some cases, the LCP 502 may communicate with the implantable cardiacpacemaker (ICP) and/or an implantable cardioverter-defibrillator (ICD).

The medical device systems 400 and 500 may also include an externalsupport device, such as external support devices 420 and 520. Theexternal support devices 420 and 520 can be used to perform functionssuch as device identification, device programming and/or transfer ofreal-time and/or stored data between devices using one or more of thecommunication techniques described herein. As one example, communicationbetween the external support device 420 and the pulse generator 406 isperformed via a wireless mode, and communication between the pulsegenerator 406 and the LCP 402 is performed via a conducted mode. In someexamples, communication between the LCP 402 and the external supportdevice 420 is accomplished by sending communication information throughthe pulse generator 406. However, in other examples, communicationbetween the LCP 402 and the external support device 420 may be via acommunication module. In some embodiments, the external support devices420, 520 may be provided with or be in communication with a display 422,522. The display 422, 522 may be a personal computer, tablet computer,smart phone, laptop computer, or other display as desired. In someinstances, the display 422, 522 may include input means for receiving aninput from a user. For example, the display 422, 522 may also include akeyboard, mouse, actuatable buttons, or be a touchscreen display. Theseare just examples.

FIGS. 4-5 illustrate two examples of medical device systems that may beconfigured to operate according to techniques disclosed herein. Otherexample medical device systems may include additional or differentmedical devices and/or configurations. For instance, other medicaldevice systems that are suitable to operate according to techniquesdisclosed herein may include additional LCPs implanted within the heart.Another example medical device system may include a plurality of LCPswithout other devices such as the pulse generator 406 or 506, with atleast one LCP capable of delivering defibrillation therapy. In yet otherexamples, the configuration or placement of the medical devices, leads,and/or electrodes may be different from those depicted in FIGS. 4 and 5.Accordingly, it should be recognized that numerous other medical devicesystems, different from those depicted in FIGS. 4 and 5, may be operatedin accordance with techniques disclosed herein. As such, the examplesshown in FIGS. 4 and 5 should not be viewed as limiting in any way.

FIG. 6 is a side view of an illustrative implantable leadless cardiacpacemaker (LCP) 610. The LCP 610 may be similar in form and function tothe LCP 100 described above. The LCP 610 may include any of the modulesand/or structural features described herein. The LCP 610 may include ashell or housing 612 having a proximal end 614 and a distal end 616. Theillustrative LCP 610 includes a first electrode 620 secured relative tothe housing 612 and positioned adjacent to the distal end 616 of thehousing 612 and a second electrode 622 secured relative to the housing612 and positioned adjacent to the proximal end 614 of the housing 612.In some cases, the housing 612 may include a conductive material and maybe insulated along a portion of its length. A section along the proximalend 614 may be free of insulation so as to define the second electrode622. The electrodes 620, 622 may be sensing and/or pacing electrodes toprovide electro-therapy and/or sensing capabilities. The first electrode620 may be capable of being positioned against or may otherwise contactthe cardiac tissue of the heart while the second electrode 622 may bespaced away from the first electrode 620. The first and/or secondelectrodes 620, 622 may be exposed to the environment outside thehousing 612 (e.g., to blood and/or tissue).

It is contemplated that the housing 612 may take a variety of differentshapes. For example, in some cases, the housing 612 may have a generallycylindrical shape. In other cases, the housing 612 may have a half-domeshape. In yet other embodiments, the housing 612 may be a rectangularprism. It is contemplated that the housing may take any cross sectionalshape desired, including but not limited to annular, polygonal, oblong,square, etc.

In some cases, the LCP 610 may include a pulse generator (e.g.,electrical circuitry) and a power source (e.g., a battery) within thehousing 612 to provide electrical signals to the electrodes 620, 622 tocontrol the pacing/sensing electrodes 620, 622. While not explicitlyshown, the LCP 610 may also include a communications module, anelectrical sensing module, a mechanical sensing module, and/or aprocessing module, and the associated circuitry, similar in form andfunction to the modules 102, 106, 108, 110 described above. The variousmodules and electrical circuitry may be disposed within the housing 612.Electrical communication between the pulse generator and the electrodes620, 622 may provide electrical stimulation to heart tissue and/or sensea physiological condition.

In the example shown, the LCP 610 includes a fixation mechanism 624proximate the distal end 616 of the housing 612. The fixation mechanism624 is configured to attach the LCP 610 to a wall of the heart H, orotherwise anchor the LCP 610 to the anatomy of the patient. As shown inFIG. 6, in some instances, the fixation mechanism 624 may include one ormore, or a plurality of hooks or tines 626 anchored into the cardiactissue of the heart H to attach the LCP 610 to a tissue wall. In otherinstances, the fixation mechanism 624 may include one or more, or aplurality of passive tines, configured to entangle with trabeculaewithin the chamber of the heart H and/or a helical fixation anchorconfigured to be screwed into a tissue wall to anchor the LCP 610 to theheart H. These are just examples.

The LCP 610 may further include a docking member 630 proximate theproximal end 614 of the housing 612. The docking member 630 may beconfigured to facilitate delivery and/or retrieval of the LCP 610. Forexample, the docking member 630 may extend from the proximal end 614 ofthe housing 612 along a longitudinal axis of the housing 612. Thedocking member 630 may include a head portion 632 and a neck portion 634extending between the housing 612 and the head portion 632. The headportion 632 may be an enlarged portion relative to the neck portion 634.For example, the head portion 632 may have a radial dimension from thelongitudinal axis of the LCP 610 that is greater than a radial dimensionof the neck portion 634 from the longitudinal axis of the LCP 610. Insome cases, the docking member 630 may further include a tetherretention structure (not explicitly shown) extending from or recessedwithin the head portion 632. The tether retention structure may definean opening configured to receive a tether or other anchoring mechanismtherethrough. The retention structure may take any shape that providesan enclosed perimeter surrounding the opening such that a tether may besecurably and releasably passed (e.g., looped) through the opening. Insome cases, the retention structure may extend though the head portion632, along the neck portion 634, and to or into the proximal end 614 ofthe housing 612. The docking member 630 may be configured to facilitatedelivery of the LCP 610 to the intracardiac site and/or retrieval of theLCP 610 from the intracardiac site. While this describes one exampledocking member 630, it is contemplated that the docking member 630, whenprovided, can have any suitable configuration.

It is contemplated that the LCP 610 may include one or more pressuresensors 640 coupled to or formed within the housing 612 such that thepressure sensor(s) is exposed to and/or otherwise operationally coupledwith the environment outside the housing 612 to measure blood pressureswithin the heart. In some cases, the one or more pressure sensors 640may be coupled to an exterior surface of the housing 612. In othercases, the one or more pressures sensors 640 may be positioned withinthe housing 612 with a pressure acting on the housing and/or a port onthe housing 612 to affect the pressure sensor 640. For example, if theLCP 610 is placed in the right ventricle, the pressure sensor(s) 640 maymeasure the pressure within the right ventricle. If the LCP 610 isplaced in another portion of the heart (such as one of the atriums orthe left ventricle), the pressures sensor(s) may measure the pressurewithin that portion of the heart. It is contemplated that the pressuresensor(s) 640 may be sensitive enough to detect a pressure change in theright atrium (e.g. atrial kick) when the LCP is placed in the rightventricle. Some illustrative pressure sensor configurations will bedescribed in more detail herein.

In some instances, the pressure sensor(s) 640 may include a deformablediaphragm formed in part or in whole from a piezoelectric material whichdoes not require external power to function. In some instances, thepressure sensor(s) 640 may include a MEMS device, such as a MEMS devicewith a pressure diaphragm with one or more piezoelectric sensors and/orpiezoresistors on the diaphragm, a capacitor-Micro-machined UltrasonicTransducer (cMUT), a condenser, a micromanometer, a surface acousticwave (SAW) device, and/or any other suitable sensor adapted formeasuring a pressure exerted on the diaphragm. Some illustrative butnon-limiting pressure sensors and configurations are describe incommonly assigned Patent Application No. 62/413,766 entitled“IMPLANTABLE MEDICAL DEVICE WITH PRESSURE SENSOR and filed on Oct. 27,2016, which is hereby incorporated by reference. It is contemplated thatwhen piezoresistors are used, a piezo-resistive bridge may be operatedin a low power mode (e.g., limited duty-cycle excitation) to reduce thepower demand of the sensor. In some cases, the gain may be modulated tofurther reduce power demands.

When a piezoelectric material is used, the piezoelectric material maygenerate an electrical voltage (and/or electric current) between a firstpressure sensor electrode and a second pressure sensor electrode inresponse to a pressure change applied to the piezoelectric material. Theelectrical voltage (and/or electric current) may be representative ofthe pressure change. In this instance, the piezoelectric material maynot require any external power, but rather the piezoelectric materialitself may convert energy extracted from the change in pressure into anelectrical voltage (and/or electric current), which can then be used bythe LCP to identify a pressure change. In some cases, it may not benecessary or even desirable to measure an absolute pressure value.Instead, just detecting a pressure change is all that is necessary toidentify certain pressure events.

The pressures sensor(s) 640 may be part of a mechanical sensing moduledescribed herein. It is contemplated that the pressure measurementsobtained from the pressures sensor(s) 640 may be used to generate apressure curve over cardiac cycles. The pressure sensor(s) 640 maymeasure/sense pressure in the chamber in which the LCP 610 is implanted.For example, an LCP 610 implanted in the right ventricle (RV) couldsense RV pressure. It is further contemplated that the pressuresensor(s) 640 may be sensitive enough to detect pressure changes inother chambers as well as the chamber in which the LCP 610 ispositioned. For example, when the LCP 610 is positioned within the rightventricle, the pressure sensor(s) 640 may detect pressure changes in theright atrium (e.g. atrial kick) in addition to pressure changes in theright ventricle.

In some cases, sensing atrial pressure events may allow the device 610to detect an atrial contraction, resulting in for example an atrialkick. Such a change in atrial pressure event may be used by an LCP inthe right ventricle to time a pacing pulse for the ventricle in supportof treating bradycardia events. In some cases, the timing of theventricle pacing pulse may be adjusted to maximize the amount of bloodentering the right ventricle through passive filling. In some instances,this may include adjusting an AV delay relative to the atrial fiducial(e.g. atrial kick). In some cases, a measured pressure change over timemay be used to support management of a CRT cardiac therapy (if placed inthe left ventricle), patient health status monitoring and/or any othersuitable goal. It is contemplated measuring pressure events in both theventricle and atrium using a single LCP may replicate a dual chambersystem with a single device. For example, such a system may enable adevice to be positioned in the ventricle while listening to both theventricle and the atrium and pacing accordingly (e.g., a VDD device).

The pressure sensor(s) 640 may be configured (either alone or incombination with other circuitry in the LCP 610) to derive a change inpressure over time and may be used to adjust atrium to ventricle (AV)pacing delay to optimize pacing for treating bradycardia events. In somecases, the pressure sensor(s) 640 may be configured to detect a-waves(e.g. atrial kick) and change the pacing timing of the LCP 610 forventricular pacing in relation to the contraction of the right atrium.It is further contemplated that sensing pressure could be used duringthe implant procedure to optimize the placement of the LCP 610 in thechamber (e.g., RV by sampling at different implant locations and usingthe best location). In some cases, frequent pressure monitoring may bebeneficial for management of heart failure patients. Frequent pressuremonitoring may also be useful for patients with chronic heart disease,hypertension, regurgitation, valve issues, atrial contraction detection,and to aid in addressing other problems. It is further contemplated thatthe pressure sensor(s) 640 may be used for monitoring respiration andassociated diseases (e.g., chronic obstructive pulmonary disease (COPD),etc.). These are just examples.

In some cases, pressure readings may be taken in combination with acardiac chamber volume measurement such an impedance measurement (e.g.,the impedance between electrodes 620 and 622) to generate apressure-impedance loop for one or more cardiac cycles. The impedancemay be a surrogate for chamber volume, and thus the pressure-impedanceloop may be representative of a pressure-volume loop for the heart H.

FIG. 7A is a plan view of the example leadless cardiac pacing device 610implanted within a right ventricle RV of the heart H during ventricularfilling. The right atrium RA, left ventricle LV, left atrium LA, andaorta A are also illustrated. FIG. 7B is a plan view of the leadlesscardiac pacing device 610 implanted within a right ventricle of theheart H during ventricular contraction. These figures illustrate how thevolume of the right ventricle may change over a cardiac cycle. As can beseen in FIGS. 7A and 7B, the volume of the right ventricle duringventricular filling is larger than the volume of the right ventricle ofthe heart during ventricular contraction.

In some cases, the processing module and/or other control circuitry maycapture, at a time point within each of one or more cardiac cycles, oneor more pressures within the heart (e.g., right ventricle and/or rightatrium), resulting in one or more pressure data points. These one ormore data points may be used, in combination with other pressure datapoints taken at different times during the one or more cardiac cycles,to generate a pressure curve. In some cases, one or more parameters maybe extracted or derived from the pressure curve. The pressure curve maybe used to facilitate cardiac resynchronization therapy (CRT), patienthealth status monitoring, and/or the management of a non-CRT cardiactherapy.

FIG. 8 is a graph 800 showing example pressures and volumes within aheart over time. More specifically, FIG. 8 depicts the aortic pressure,left ventricular pressure, left atrial pressure, left ventricularvolume, an electrocardiogram (ECG or egram), and heart sounds of theheart H. A cardiac cycle may begin with diastole, and the mitral valveopens. The ventricular pressure falls below the atrial pressure,resulting in the ventricular filling with blood. During ventricularfilling, the aortic pressure slowly decreases as shown. During systole,the ventricle contracts. When ventricular pressure exceeds the atrialpressure, the mitral valve closes, generating the S1 heart sound. Beforethe aortic valve opens, an isovolumetric contraction phase occurs wherethe ventricle pressure rapidly increases but the ventricular volume doesnot significantly change. Once the ventricular pressure equals theaortic pressure, the aortic valve opens and the ejection phase beginswhere blood is ejected from the left ventricle into the aorta. Theejection phase continues until the ventricular pressure falls below theaortic pressure, at which point the aortic valve closes, generating theS2 heart sound. At this point, the isovolumetric relaxation phase beginsand ventricular pressure falls rapidly until it is exceeded by theatrial pressure, at which point the mitral valve opens and the cyclerepeats. Contractions of the atria are initiated near the end ofventricular diastole. The active atrial contraction pushes or forcesadditional volumes of blood into the ventricles (often referred to as“atrial kick”) in addition to the volumes associated with passivefilling. In some cases, the atrial kick contributes in the range ofabout 20% of the volume of blood toward ventricular preload. At normalheart rates, the atrial contractions are considered essential foradequate ventricular filling. However, as heart rates increase, atrialfilling becomes increasingly important for ventricular filling becausethe time interval between contractions for passive filling becomesprogressively shorter. Cardiac pressure curves for the pulmonary artery,the right atrium, and the right ventricle, and the cardiac volume curvefor the right ventricle, similar to those illustrated in FIG. 8 for theleft part of the heart, may be likewise generated. Typically, thecardiac pressure in the right ventricle is lower than the cardiacpressure in the left ventricle.

In one example, the heart sound signals can be recorded using acousticsensors, (for example, a microphone), which capture the acoustic wavesresulted from heart sounds. In another example, the heart sound signalscan be recorded using accelerometers or pressure sensors that capturethe accelerations or pressure waves caused by heart sounds. The heartsound signals can be recorded within or outside the heart. These arejust examples.

FIG. 9 is a cross-section of an illustrative implantable leadlesscardiac pacemaker (LCP) 900. The LCP 900 may be similar in form andfunction to the LCPs 100, 610 described above. The LCP 900 may includeany of the modules and/or structural features described above withrespect to the LCPs 100, 610. The LCP 900 may include a shell or housing902 having a proximal end 904 and a distal end 906. In the exampleshown, the LCP 900 does not include a docking member. However, in somecases, a docking member may be provided, such as a cage, a head or otherfeature extending proximally from adjacent the side walls of the housing902. The illustrative LCP 900 includes a first electrode 908 securedrelative to the housing 902 and positioned adjacent to the distal end906 of the housing 902, and a second electrode (not explicitly shown)secured relative to the housing 902 and positioned adjacent to theproximal end 904 of the housing 902. In some instances, the firstelectrode 908 may be positioned on a distal end surface facing distally.In some cases, the housing 902 may include a conductive material and maybe insulated along a portion of its length. A section along the proximalend 904 may be free of insulation so as to define the second electrode.The electrodes 908 may be sensing and/or pacing electrodes to aid inproviding electro-therapy and/or sensing capabilities. The firstelectrode 908 may be capable of being positioned against or mayotherwise contact the cardiac tissue of the heart while the secondelectrode may be spaced away from the first electrode 908. The firstand/or second electrodes 908 may be exposed to the environment outsidethe housing 902 (e.g., to blood and/or tissue).

In some cases, the LCP 900 may include a pulse generator (e.g.,electrical circuitry) 910 and a power source (e.g., a battery) 912within the housing 902 to provide and/or receive electrical signals viathe first and second electrodes. While not explicitly shown in FIG. 9,the LCP 900 may also include a communications module, an electricalsensing module, a mechanical sensing module, and/or a processing module,and associated circuitry, similar in form and function to the modules102, 106, 108, 110 described above. The various modules and electricalcircuitry may be disposed within the housing 902. Electricalcommunication between the pulse generator and the electrodes may provideelectrical stimulation to heart tissue and/or sense a physiologicalcondition.

In the example shown, the LCP 900 further includes a fixation mechanism914 proximate the distal end 906 of the housing 902. The fixationmechanism 914 is configured to attach the LCP 900 to a wall of the heartH, or otherwise anchor the LCP 900 to the anatomy of the patient. Asshown in FIG. 9, in some instances, the fixation mechanism 914 mayinclude one or more, or a plurality of hooks or tines 916 anchored intothe cardiac tissue of the heart H to attach the LCP 900 to a tissuewall. In other instances, the fixation mechanism 914 may include one ormore, or a plurality of passive tines, configured to entangle withtrabeculae within the chamber of the heart H and/or a helical fixationanchor configured to be screwed into a tissue wall to anchor the LCP 900to the heart H. These are just examples.

The housing 902 may include a proximal end surface 918 facing proximally(e.g., in a generally opposite direction from the distal end surface. Insome instances, the proximal end surface 918 of the housing 902 may forma diaphragm 920. In some cases, the diaphragm 920 may be formed from thehousing material itself. When so provided, the wall thickness of thehousing in the region of the diaphragm 920 may be thinned to increasethe flexibility of the diaphragm 920 to as to be responsive (e.g.sufficiently deformable) to a pressure range of interest. In othercases, the diaphragm 920 may be formed from another material, such asbut not limited to titanium, titanium foil, silicone, polyimides, etc.to form a deformable or movable diaphragm 920 that is responsive to apressure of interest applied to the diaphragm 920. In some instances,the diaphragm 920 may be titanium or titanium foil on polyvinylidenefluoride (PVDF). In some instances, the diaphragm 920 may be formed froma piezoelectric material and/or may include a piezoelectric layer.

A piezoelectric material may exhibit the piezoelectric effect, or theability to generate a voltage (and/or current) when the material issubjected to a mechanical stress or vibration. Some illustrativepiezoelectric materials may include, but are not limited to somenaturally occurring crystals (e.g., quartz, sucrose, Rochelle salt,topaz, lead titanate, etc.), synthetic crystals, ceramics (e.g., bariumtitanate, lead zirconate titanate (PZT), zinc oxide, etc.), polymers(e.g., polyvinylidene fluoride (PVDF)), etc. This list is not intendedto be exhaustive of all types of piezoelectric materials, but ratherillustrative of some example materials. When used as part of thehermetic seal around the LCP, it is contemplated that the material(piezoelectric or otherwise) selected for the diaphragm 920 may behermetic. For example, the material should be capable of preventingblood from diffusing through the diaphragm and into the interior or theLCP.

In any event, the diaphragm 920 may be fabricated to flex or deform asthe pressure (external to the housing 902) in the heart (e.g., rightventricle and/or right atrium) changes, as will be described in moredetail herein. While the entire proximal end surface 918 may form thediaphragm 920, it is contemplated that only a portion of the end surface918 may form the diaphragm 920. In some cases, the diaphragm 920 may be1 millimeter in diameter or less. In other cases, the diaphragm 920 maybe greater than 1 millimeter in diameter. In some cases, the diaphragm920 may have a round shape. In other cases, the diaphragm 920 may have asquare, rectangular or any other suitable shape. In some cases, thediaphragm 920 may not have a uniform thickness. In some cases, thediaphragm 920 may have thicker bossed regions that provide support to,for example, increase the linearity of the deformation of the diaphragm920 with pressure.

In some cases, the diaphragm 920 may be formed from a piezoelectricmaterial. As the diaphragm flexes or deforms in response to an externalpressure, a voltage (and/or current) may be generated by thepiezoelectric material between sensor electrodes on opposing sides ofthe piezoelectric material. The generated voltage (and/or current) maybe transferred via one or more electrical conductors 924 to theelectrical circuitry 910, which may identify a pressure event and/orpressure value. In some cases, the generated voltage (and/or current)may reflect a change in pressure over time as opposed to an absolute orgauge pressure. When so provided, a reference pressure may not berequired. In any event, the change in pressure over time may besufficient to identify events such as the atrial contraction (e.g.,atrial kick), ventricular filling, ventricular ejection, etc. In someinstances, the electrical circuitry 910 may be configured to obtainpressure measurements at a sample rate of greater than 100 Hertz (Hz),but this is not required. This may allow for pressure measurements to beused to determine characteristics of the cardiac cycle including, butnot limited to, dP/dT, dicrotic notch, etc.

In some cases, the one or more electrical conductors 924 may include afirst electrical conductor coupled to a first electrode on a first sideof the piezoelectric material, and a second electrical conductor coupleda second electrode on a second opposite side of the piezoelectricmaterial, such that the voltage (and/or current) generated istransmitted to the electrical circuitry 910.

The diaphragm 920 need not be placed on the proximal end surface 918 ofthe housing 902 such as shown in FIG. 9. It is contemplated that thediaphragm 920 may be formed in any surface that is exposed to theenvironment outside of the housing 902. In some cases, locating thediaphragm 920 on or adjacent to the proximal end 904 of the housing 902may orientate the diaphragm towards the heart valves (when the LCP 900is positioned in the apex of the heart) and in-line with expectedmaximum pressure changes within the heart, which may achieve highersignal-to-noise (SN) levels. This may also locate the diaphragm 920 awayfrom the heart wall, which may reduce the likelihood that the diaphragm920 will become fibrossed-over. In some cases, the diaphragm 920 may becoated with an anti-thrombogenic coating to help prevent tissue growthon or over the diaphragm 920.

In the example of FIG. 9, a battery 912 is shown adjacent the diaphragm920. However, many different configurations of the internal componentsof the LCP 900 are contemplated. In the example shown, the processingmodule (e.g., circuitry or control electronics) 910 is positioned in adistal portion 906 of the housing 902 adjacent to the distal electrode.The one or more electrical conductors 924 may be formed of a polyimideor similar interconnect having a cross-sectional dimension in the rangeof less than 250 microns. It is contemplated that the inside surface ofthe housing 902 may be electrically insulated and the electricalconductors 924 (e.g., trace) may be positioned on the inside surface ofthe housing 902 or along the outer surface of the battery 912, asdesired. Alternatively, wires or a ribbon cable may be used. These arejust examples.

In some cases, the electrical circuitry 910 may be configured to obtainpressure measurements at predetermined intervals over one or morecardiac cycles. In other instances, the electrical circuitry 910 may beconfigured to obtain a pressure measurement in response to a specificcardiac event or at a specific time in a cardiac cycle. For example, thecircuitry 910 may be configured to use one or more cardiac signalssensed by the first electrode 908 and/or second electrode to determinewhen the patient's heart is in a first phase of a cardiac cycle. Thecircuitry 910 may be configured to determine a pressure exterior to thehousing 902 based at least in part on the pressure obtained during thefirst phase of the cardiac cycle. In some cases, the first phase may besystole and in other cases the first phase may be diastole. Thecircuitry 910 may also be configured to determine a pressure exterior tothe housing 902 based at least in part on the pressure taken during asecond phase of the cardiac cycle. It is contemplated that the circuitry910 may be further configured to detect heart sounds of the patient'sheart based at least in part on the pressure sensor output signal. Forexample, the first heart sound may be a timing fiducial for a suddenincrease in pressure while the second heart sound may be a timingfiducial for a sudden decrease in pressure.

In some cases, the circuitry 910 of the LCP 900 may be configured toobtain a plurality of pressure readings over one or more cardiac cycles.The pressure readings may be plotted (either by the circuitry 910 or anexternal device) to form a graph similar to the one shown in FIG. 8.Various parameters related to the function of the heart can beextrapolated from the graph including but not limited to peak to peakmeasurements, dP/dT, time averaged values, inotropic response of theventricle, etc. In some instances, the pressure measurements may becompared to calibration values (e.g., measurements taken at the time ofimplantation of the LCP 900). It is further contemplated that thediaphragm 920 may be sensitive enough to generate a voltage in responseto a pressure increase in a chamber different from the chamber in whichthe LCP 900 is implanted. For example, when the LCP 900 is implanted inthe right ventricle, the diaphragm may generate a voltage in response toa pressure increase in the right atrium (e.g. atrial kick) as well as apressure increase in the right ventricle.

In some cases, the diaphragm 920 may be formed of the same material andof the same thickness as the remaining portion of the housing 902. Forexample, the housing 902 may flex or deform to transfer a pressureexternal to the housing 902 to a layer of piezoelectric material locatedwithin the housing 612. For example, the housing 902 may have acompliance such that the relative movement of the housing 902 inresponse to the external pressure may be operatively coupled to apiezoelectric material. The resulting voltage (and/or current) generatedby the piezoelectric material may be calibrated relative to externalpressures prior to implantation of the LCP 900 in a patient. Thecalibration data may be stored in the memory and/or electrical circuitryof the LCP 900. In some cases, there may be some pressure loss (e.g., inthe range of 1-20% or more) between the pressure exerted on the housing902 and the pressure applied to the piezoelectric material, depending onthe placement of the piezoelectric material. This pressure loss may becompensated for (e.g., nullified) by adjusting the algorithm thatconverts the voltage (and/or current) generated by the piezoelectricmaterial to a pressure using the calibration data stored in the LCP 900.

FIG. 10 illustrates a proximal end portion 954 of another illustrativeLCP 950 having a diaphragm 960 and a piezoelectric membrane 962. The LCP950 may be similar in form and function to the LCPs 100, 610, 900described above. The LCP 950 may include any of the modules and/orstructural features described above with respect to the LCPs 100, 610,900.

The illustrative LCP 950 may include a shell or housing 952 having aproximal end portion 954 and a distal end (not explicitly shown). Thehousing 952 may include a proximal end surface 956 facing proximally(e.g., in a generally opposite direction from the distal end surface).In some instances, the proximal end surface 956 of the housing 952 mayform a diaphragm 960. In some cases, the diaphragm 960 may be formedfrom the housing material itself, but this is not required. When soprovided, the wall thickness of the housing in the region of thediaphragm 960 may be thinned to increase the flexibility of thediaphragm 960, although this is not required. In some cases, thediaphragm 960 may be formed from another material, such as but notlimited to titanium, titanium foil, silicone, polyimides, etc. to form adeformable or movable diaphragm 960 that is responsive to a desiredpressure range applied to the diaphragm 960.

In the example shown, the diaphragm 960 may flex or deform and transfera pressure applied from external to the housing 952 to a layer ofpiezoelectric material 962 located within the housing 952. For example,the housing 952 may have a compliance such that the relative movement ofthe housing 952 and/or diaphragm 960 in response to the externalpressure may deform or otherwise apply a corresponding stress to apiezoelectric material or membrane 962. In some embodiments, thepiezoelectric membrane 962 may be coupled to or positioned on aninterior surface of the diaphragm 960, although this is not required.

As the diaphragm 960 flexes in response an external pressure, thepiezoelectric membrane 962 may also flex. The applied stress to thepiezoelectric membrane 962 may generate a voltage (and/or a current)between a first sensor electrode on one side of the piezoelectricmembrane 962 and a second sensor electrode on the opposing side of thepiezoelectric membrane 962. The voltage (and/or current) may betransferred via one or more electrical conductors 964 to the electricalcircuitry of the LCP 950 where it may be converted from a voltage(and/or current) to a pressure reading. In some cases, the one or moreelectrical conductors 964 may include a first electrical conductorcoupled to a first side of the piezoelectric membrane 962 and a secondelectrical conductor coupled a second side, opposite of the first sidesuch that the voltage (and/or current) generated is transmitted to theelectrical circuitry. In some instances, the electrical conductors maybe coupled to the first and second sensor electrodes generally shown at968.

The voltage (and/or current) generated by the piezoelectric material maybe calibrated relative to external pressures applied prior toimplantation of the LCP 950 in a patient. The calibration data may bestored in the memory and/or electrical circuitry of the LCP 950. In somecases, there may be some pressure loss (e.g., in the range of 1-20% ormore) between the pressure exerted on the housing 952 and the pressureapplied to the piezoelectric membrane 962. This pressure loss may becompensated for (e.g., nullified) by adjusting the algorithm thatconverts the voltage (and/or current) generated by the piezoelectricmembrane 962 to a pressure using the calibration data stored in the LCP950.

In the example of FIG. 10, the battery 966 is shown adjacent thediaphragm 960. However, many different configurations of the internalcomponents of the LCP 950 are contemplated. In the example shown, theprocessing module (e.g., circuitry or control electronics) may bepositioned in a distal portion of the housing 952 adjacent to the distalelectrode. The one or more electrical conductors 964 may be formed of apolyimide or similar interconnect having a cross-sectional dimension inthe range of less than 250 microns. It is contemplated that the insidesurface of the housing 952 may be electrically insulated and theelectrical conductors 964 (e.g., trace) may be positioned on the insidesurface of the housing 952 or along the outer surface of the battery966, as desired. Alternatively, wires or a ribbon cable may be used.These are just examples.

FIG. 11 illustrates a proximal end portion 1004 of another illustrativeLCP 1000 having a diaphragm 1006 and a piezoelectric membrane 1010. TheLCP 1000 may be similar in form and function to the LCPs 100, 610, 900described above. The LCP 1000 may include any of the modules and/orstructural features described above with respect to the LCPs 100, 610,900.

The illustrative LCP 1000 may include a shell or housing 1002 having aproximal end portion 1004 and a distal end (not explicitly shown). Thehousing 1002 may include a proximal end surface 1018 facing proximally(e.g., in a generally opposite direction from the distal end surface).In some instances, the proximal end surface 1018 of the housing 1002 mayform a diaphragm 1006. In some cases, the diaphragm 1006 may be formedfrom the housing material itself, although this is not required. When soprovided, the wall thickness of the housing in the region of thediaphragm 1006 may be thinned to increase the flexibility of thediaphragm 1006, although this is not required. In some cases, thediaphragm 1006 may be formed from another material, such as but notlimited to titanium, titanium foil, silicone, polyimides, etc. to form adeformable or movable diaphragm 1006 that is responsive to a desiredpressure range applied to the diaphragm 1006.

The diaphragm 1006 may flex or deform to transfer a pressure external tothe housing 1002 to a layer of piezoelectric material or a piezoelectricmembrane 1010 located within the housing 1002. For example, the housing1002 may have a compliance such that the relative movement of thehousing 1002 and/or diaphragm 1006 in response to the external pressuremay be mechanically coupled to a piezoelectric material or membrane1010. In some embodiments, the piezoelectric membrane 1010 may becoupled to the diaphragm 1006 via a mechanical linkage or arm 1008. Thismay allow the piezoelectric membrane 1010 to be spaced a distance fromthe housing 1002 while still flexing in response to an externallyapplied pressure 1016. In some cases, it may be desirable for a morerigid piezoelectric material to be used, and the mechanical leverageprovide by the mechanical linkage or arm 1008 may allow a more modestexternal pressure applied to the diaphragm 1006 to suitable stress thepiezoelectric membrane 1010 to produce a desired voltage (and/orcurrent). In the example shown, as the diaphragm 1006 flexes in responsethe external pressure 1016, the linkage 1008 also moves and transfersthe force to the piezoelectric membrane 1010. The force applied to thepiezoelectric membrane 1010 generates an voltage (and/or a current),which may be transferred via one or more electrical conductors 1012 tothe electrical circuitry of the LCP 1000 where it is converted from anvoltage (and/or current) to a pressure reading. In some cases, the oneor more electrical conductors 1012 may include a first electricalconductor coupled to a first side of the piezoelectric membrane 1010 anda second electrical conductor coupled a second side, opposite of thefirst side of the piezoelectric membrane 1010, such that the voltage(and/or current) generated across the piezoelectric membrane 1010 istransmitted to the electrical circuitry. In some instances, theelectrical conductors may be coupled to first and second pressure sensorelectrodes positioned on opposite sides of the piezoelectric membrane1010.

The voltage generated by the piezoelectric membrane 1010 may becalibrated relative to external pressures prior to implantation of theLCP 1000 in a patient. The calibration data may be stored in the memoryand/or electrical circuitry of the LCP 1000. In some cases, there may besome pressure loss (e.g., in the range of 1-20% or more) between thepressure exerted on the housing 1002 and the pressure applied to thepiezoelectric membrane 1010, depending on the linkage or arm 1008. Thispressure loss may be compensated for (e.g., nullified) by adjusting thealgorithm that converts the voltage (and/or current) generated by thepiezoelectric material to a pressure using the calibration data storedin the LCP 1000.

In the example shown in FIG. 11, the battery 1014 is shown adjacent thepiezoelectric membrane 1010. However, many different configurations ofthe internal components of the LCP 1000 are contemplated. In the exampleshown, the processing module (e.g., circuitry or control electronics)may be positioned in a distal portion of the housing 1002 adjacent tothe distal electrode. The one or more electrical conductors 1012 may beformed of a polyimide or similar interconnect having a cross-sectionaldimension in the range of less than 250 microns. It is contemplated thatthe inside surface of the housing 1002 may be electrically insulated andthe electrical conductors 1012 (e.g., trace) may be positioned on theinside surface of the housing 1002 or along the outer surface of thebattery 1014, as desired. Alternatively, wires or a ribbon cable may beused. These are just examples.

FIG. 12 illustrates a proximal end portion 1054 of another illustrativeLCP 1050 having a diaphragm 1056 and a piezoelectric membrane 1062. Theillustrative LCP 1050 may be similar in form and function to the LCPs100, 610, 900 described above. The LCP 1050 may include any of themodules and/or structural features described above with respect to theLCPs 100, 610, 900.

The illustrative LCP 1050 may include a shell or housing 1052 having aproximal end portion 1054 and a distal end (not explicitly shown). Thehousing 1052 may include a proximal end surface 1066 facing proximally(e.g., in a generally opposite direction from the distal end surface).In some instances, the proximal end surface 1066 of the housing 1052 mayform a diaphragm 1056. In some cases, the diaphragm 1056 may be formedfrom the housing material itself, but this is not required. When soprovided, the wall thickness of the housing in the region of thediaphragm 1056 may be thinned to increase the flexibility of thediaphragm 1056, although this is not required. In other cases, thediaphragm 1056 may be formed from another material, such as but notlimited to titanium, titanium foil, silicone, polyimides, etc. to form adeformable or movable diaphragm 1056 that is responsive to a desiredpressure range applied to the diaphragm 1056.

The diaphragm 1056 may flex or deform to transfer a pressure external tothe housing 1052 to a layer of piezoelectric material or a piezoelectricmembrane 1062 located within the housing 1052. In the example shown, acavity 1064 filled with a fluid 1068 may be positioned between theexternal diaphragm 1056 and an internal diaphragm 1058. The fluid filledcavity 1064 may be in fluid communication with the diaphragm(s) 1056,1058 such that the fluid filled cavity 1064 may communicate a measurerelated to the pressure 1070 applied by the environment to the diaphragm1056 of the housing 1052 ultimately to piezoelectric membrane 1062. Thefluid filled cavity 1064 may be filled with an incompressible fluid1068. In some cases, the fluid filled cavity 1064 may be filled with anon-conductive fluid 1068. In some cases, the fluid 1068 may be highlysoluble to gases that may arise inside of the housing, particularly atbody temperature (e.g., 37° C.). For example, the fluid 1068 may behighly soluble to hydrogen, helium, nitrogen, argon, water, and/or othergases or liquids that might arise inside of the housing as a result of,for example, outgassing of internal components of the LCP 1050.

The diaphragms 1056, 1058 may have a compliance such that the relativemovement of the housing 1052 and/or diaphragm 1056 in response to theexternal pressure may be coupled to the piezoelectric material ormembrane 1062, sometimes through a mechanical linkage or arm 1060. InFIG. 12, the piezoelectric membrane 1062 is shown mechanically coupledto the inner diaphragm 1058 via a mechanical linkage or arm 1060.However, it is contemplated that the piezoelectric material or membrane1062 may be adhered directly to the inner diaphragm 1058, or the innerdiaphragm 1058 may be made from or otherwise form the piezoelectricmaterial or membrane 1062.

As the diaphragm 1056 flexes in response the external pressure 1070,force is transferred 1072 through the fluid filled cavity 1064 to theinner diaphragm 1058. The inner diaphragm 1058 then transfers the forceto the piezoelectric material or membrane 1062, sometimes through amechanical linkage or arm 1060. The force applied to the piezoelectricmembrane 1062 generates an voltage (and/or s current). The voltage(and/or current) may be transferred via one or more electricalconductors 1074 to the electrical circuitry of the LCP 1050 where it isconverted from a voltage (and/or a current) to a pressure reading.

In some cases, the one or more electrical conductors 1024 may include afirst electrical conductor coupled to a first side of the piezoelectricmembrane 1062 and a second electrical conductor coupled a second side,opposite of the first side of the piezoelectric membrane 1062, such thatthe voltage (and/or current) generated across the piezoelectric membrane1062 is transmitted to the electrical circuitry. In some instances, theelectrical conductors may be coupled to first and second pressure sensorelectrodes positioned on opposite sides of the piezoelectric membrane1062.

The voltage generated by the piezoelectric material may be calibratedrelative to external pressures applied prior to implantation of the LCP1050 in a patient. The calibration data may be stored in the memoryand/or electrical circuitry of the LCP 1050. In some cases, there may besome pressure loss (e.g., in the range of 1-20% or more) between thepressure exerted on the housing 1052 and the pressure applied to thepiezoelectric membrane 1062. This pressure loss may be compensated for(e.g., nullified) by adjusting the algorithm that converts the voltage(and/or current) generated by the piezoelectric material to a pressureusing the calibration data stored in the LCP 1050.

In the example of FIG. 12, the battery 1076 is shown adjacent thepiezoelectric membrane 1062. However, many different configurations ofthe internal components of the LCP 1050 are contemplated. In the exampleshown, the processing module (e.g., circuitry or control electronics)may be positioned in a distal portion of the housing 1052 adjacent tothe distal electrode. The one or more electrical conductors 1074 may beformed of a polyimide or similar interconnect having a cross-sectionaldimension in the range of less than 250 microns. It is contemplated thatthe inside surface of the housing 1052 may be electrically insulated andthe electrical conductors 1074 (e.g., trace) may be positioned on theinside surface of the housing 1052 or along the outer surface of thebattery 1076, as desired. Alternatively, wires or a ribbon cable may beused. These are just examples.

FIG. 13 illustrates a proximal end portion 1104 of another illustrativeLCP 1100 having a diaphragm 1106 and a piezoelectric membrane 1108. TheLCP 1100 may be similar in form and function to the LCPs 100, 610, 900described above. The LCP 1100 may include any of the modules and/orstructural features described above with respect to the LCPs 100, 610,900.

The LCP 1100 may include a shell or housing 1102 having a proximal endportion 1104 and a distal end (not explicitly shown). The housing 1102may include a proximal end surface 1110 facing proximally (e.g., in agenerally opposite direction from the distal end surface). In someinstances, the proximal end surface 1110 of the housing 1102 may form adiaphragm 1106. In some cases, the diaphragm 1106 may be formed from thehousing material itself, but this is not required. When so provided, thewall thickness of the housing in the region of the diaphragm 1106 may bethinned to increase the flexibility of the diaphragm 1106, although thisis not required. In some cases, the diaphragm 1106 may be formed fromanother material, such as but not limited to titanium, titanium foil,silicone, polyimides, etc. to form a deformable or movable diaphragm1106 that is responsive to a desired pressure range applied to thediaphragm 1106.

The diaphragm 1106 may flex or deform to transfer a pressure external tothe housing 1102 to a layer of piezoelectric material or a piezoelectricmembrane 1108 located within the housing 1102. In some embodiments, acavity 1112 filled with a fluid 1114 may be positioned between thediaphragm 1106 and the piezoelectric membrane 1108. The fluid filledcavity 1112 is shown in fluid communication with the diaphragm 1106 suchthat the fluid filled cavity 1112 may communicate a measure related tothe pressure 1116 applied by the environment to the piezoelectricmembrane 1108. The fluid filled cavity 1112 may be filled with anincompressible fluid 1114. In some cases, the fluid filled cavity 1112may be filled with a non-conductive fluid 1114. In some cases, the fluid1114 may be highly soluble to gases that may be inside of the housing,particularly at body temperature (e.g., 37° C.). For example, the fluid1114 may be highly soluble to hydrogen, helium, nitrogen, argon, water,and/or other gases or liquids that might arise inside of the housing asa result of, for example, outgassing of internal components of the LCP1100.

The diaphragm 1106 may have a compliance such that the relative movementof the housing 1102 and/or diaphragm 1106 in response to a desired rangeof external pressures is coupled 1118 to the piezoelectric material ormembrane 1108 though the fluid 1114. The force 1118 applied to thepiezoelectric membrane 1108 may generate a voltage (and/or a current).The voltage (and/or current) may be transferred via one or moreelectrical conductors 1120 to the electrical circuitry of the LCP 1100where it may be converted from a voltage (and/or current) to a pressurereading. It is contemplated that in some instances, the piezoelectricmembrane 1108 may be formed from a piezoelectric material or have apiezoelectric material formed on a surface of another flexible materialas described with respect to, for example, FIG. 10.

In some cases, the one or more electrical conductors 1120 may include afirst electrical conductor coupled to a first side of the piezoelectricmembrane 1108 and a second electrical conductor coupled a second side,opposite of the first side of the piezoelectric membrane 1108, such thatthe voltage (and/or current) generated by the piezoelectric material ormembrane 1108 is transmitted to the electrical circuitry. In someinstances, the electrical conductors may be coupled to first and secondpressure sensor electrodes positioned on opposite sides of thepiezoelectric membrane 1108.

The voltage (and/or current) generated by piezoelectric membrane 1108may be calibrated relative to external pressures applied prior toimplantation of the LCP 1100 in a patient. The calibration data may bestored in the memory and/or electrical circuitry of the LCP 1100. Insome cases, there may be some pressure loss (e.g., in the range of 1-20%or more) between the pressure exerted on the housing 1102 and thepressure applied to the piezoelectric membrane 1108. This pressure lossmay be compensated for (e.g., nullified) by adjusting the algorithm thatconverts the voltage (and/or current) generated by the piezoelectricmembrane 1108 to a pressure using the calibration data stored in the LCP1100.

In the example of FIG. 13, the battery 1122 is shown adjacent thepiezoelectric membrane 1108. However, many different configurations ofthe internal components of the LCP 1100 are contemplated. In the exampleshown, the processing module (e.g., circuitry or control electronics)may be positioned in a distal portion of the housing 1102 adjacent tothe distal electrode. The one or more electrical conductors 1120 may beformed of a polyimide or similar interconnect having a cross-sectionaldimension in the range of less than 250 microns. It is contemplated thatthe inside surface of the housing 1102 may be electrically insulated andthe electrical conductors 1120 (e.g., trace) may be positioned on theinside surface of the housing 1102 or along the outer surface of thebattery 1122, as desired. Alternatively, wires or a ribbon cable may beused. These are just examples.

FIG. 14 illustrates a cross-sectional view of a proximal end portion1154 of another illustrative LCP 1150 having a diaphragm 1156 andpiezoelectric membrane 1158. The LCP 1150 may be similar in form andfunction to the LCPs 100, 610, 900 described above. The LCP 1150 mayinclude any of the modules and/or structural features described abovewith respect to the LCPs 100, 610, 900.

The LCP 1150 may include a shell or housing 1152 having a proximal endportion 1154 and a distal end (not explicitly shown). In this example,the housing 1152 includes a docking member 1160 extending proximallyfrom the proximal end portion 1154. The docking member 1160 may beconfigured to facilitate delivery and/or retrieval of the LCP 1150. Forexample, the docking member 1160 may extend from the proximal endportion 1154 of the housing 1152 along a longitudinal axis of thehousing 1152. The docking member 1160 may include a head portion 1162and a neck portion 1164 extending between the housing 1152 and the headportion 1162. The head portion 1162 may be an enlarged portion relativeto the neck portion 1164. An access port 1166 may extend through thehead portion 1162 and the neck portion 1164 to fluidly couple thediaphragm 1156 with the blood in the heart. The diaphragm 1156 may beconstructed using any of the materials and/or configurations describedherein. In some cases, the diaphragm 1156 may be positioned at theproximal opening 1168 of the access port 1166.

It is contemplated that the docking member 1160 may be formed as aseparate structure from the housing 1152 and subsequently attached tothe housing 1152. For example, the docking member 1160 may be 3-D metalstructure that is welded (or otherwise coupled or secured) to thehousing 1152. In other embodiments, the docking member 1160 and thehousing 1152 may be formed as a single monolithic structure.

A piezoelectric membrane 1158 may be positioned adjacent to, but notnecessarily in direct contact with the diaphragm 1156. In some cases,the piezoelectric membrane 1158 may be positioned directly on an innersurface of the diaphragm 1156, such as described with respect to FIG.10. In other embodiments, the piezoelectric membrane 1158 may bemechanically and/or fluidly coupled to the diaphragm 1156 through amechanical linkage and/or a fluid filled chamber, similar to thatdescribed above. As the diaphragm 1156 flexes in response the anexternal pressure, the piezoelectric membrane 1158 may also flex. Thestress on the piezoelectric membrane 1158 may generate a voltage (and/orcurrent). The voltage (and/or current) may be transferred via one ormore electrical conductors 1170 to the electrical circuitry of the LCP1150 where it is converted from a voltage (and/or current) to a pressurereading. In some embodiments, the piezoelectric membrane 1158 may beoperatively connected to the housing 1152 which in turn is operativelycoupled to the circuitry or control electronics.

In some cases, the one or more electrical conductors 1170 may include afirst electrical conductor coupled to a first side of the piezoelectricmembrane 1158 and a second electrical conductor coupled a second side,opposite of the first side of the piezoelectric membrane 1158, such thatthe voltage (and/or current) generated across the piezoelectric membrane1158 is transmitted to the electrical circuitry. In some instances, theelectrical conductors may be coupled to first and second pressure sensorelectrodes positioned on opposite sides of the piezoelectric membrane1158.

FIG. 14 illustrates the battery 1172 adjacent to the piezoelectricmembrane 1158. However, many different configurations of the internalcomponents of the LCP 1150 are contemplated. The one or more electricalconductors 1170 may be formed of a polyimide or similar interconnecthaving a cross-sectional dimension in the range of less than 250microns. It is contemplated that the inside surface of the housing 1152may be electrically insulated and the electrical conductors 1170 (e.g.,trace) positioned on the inside surface of the housing 1152 or along theouter surface of the battery 1172, as desired. Alternatively, wires or aribbon cable may be used. These are just examples.

FIG. 15 illustrates a cross-sectional view of a proximal end portion1204 of another illustrative LCP 1200 having a diaphragm 1206 and apiezoelectric membrane 1208. The LCP 1200 may be similar in form andfunction to the LCPs 100, 610, 900 described above. The LCP 1200 mayinclude any of the modules and/or structural features described abovewith respect to the LCPs 100, 610, 900.

The LCP 1200 may include a shell or housing 1202 having a proximal endportion 1204 and a distal end (not explicitly shown). The housing 1202may include a docking member 1210 extending proximally from the proximalend portion 1204. The docking member 1210 may be configured tofacilitate delivery and/or retrieval of the LCP 1200. For example, thedocking member 1210 may extend from the proximal end portion 1204 of thehousing 1202 along a longitudinal axis of the housing 1202. The dockingmember 1210 may include a head portion 1212 and a neck portion 1214extending between the housing 1202 and the head portion 1212. The headportion 1212 may be an enlarged portion relative to the neck portion1214. An access port 1216 may extend through the head portion 1212 andthe neck portion 1214 to fluidly couple the diaphragm 1206 with theblood in the heart. The diaphragm 1206 may be constructed using any ofthe materials and/or configurations described herein. In some cases, thediaphragm 1206 may be positioned at the proximal opening 1168 of theaccess port 1216.

It is contemplated that the docking member 1210 may be formed as aseparate structure from the housing 1202 and subsequently attached tothe housing 1202. For example, the docking member 1210 may be 3-D metalstructure that is welded (or otherwise coupled or secured) to thehousing 1202. In other embodiments, the docking member 1210 and thehousing 1202 may be formed as a single monolithic structure.

A piezoelectric membrane 1208 may be positioned adjacent to, but notnecessarily in direct contact with the diaphragm 1206. In someembodiments, the piezoelectric membrane 1208 may be coupled to thediaphragm 1206 via a mechanical linkage or arm 1218. At least part ofthe piezoelectric membrane 1208 may be held in place relative to thehousing 1202 such that movement of the diaphragm 1206 and mechanicallinkage or arm 1218 relative to the piezoelectric membrane 1208 inducesa stress in the piezoelectric membrane 1208. As the diaphragm 1206flexes in response the external pressure 1220, the linkage 1218 movesand transfers the force to the piezoelectric membrane 1208. The forceapplied to the piezoelectric membrane 1208 generates a voltage (and/orcurrent). The voltage (and/or current) may be transferred via one ormore electrical conductors 1222 to the electrical circuitry of the LCP1000 where it is converted from a voltage (and/or current) to a pressurereading.

In some cases, the one or more electrical conductors 1222 may include afirst electrical conductor coupled to a first side of the piezoelectricmembrane 1208 and a second electrical conductor coupled a secondopposite side of the piezoelectric membrane 1208 such that the voltage(and/or current) generated across the piezoelectric membrane 1208 istransmitted to the electrical circuitry. In some instances, theelectrical conductors may be coupled to first and second pressure sensorelectrodes positioned on opposite sides of the piezoelectric membrane1208.

FIG. 15 illustrates the battery 1224 adjacent to the piezoelectricmembrane 1208. However, many different configurations of the internalcomponents of the LCP 1200 are contemplated. The one or more electricalconductors 1222 may be formed of a polyimide or similar interconnecthaving a cross-sectional dimension in the range of less than 250microns. It is contemplated that the inside surface of the housing 1202may be electrically insulated and the electrical conductors 1222 (e.g.,trace) positioned on the inside surface of the housing 1202 or along theouter surface of the battery 1224, as desired. Alternatively, wires or aribbon cable may be used. These are just examples.

It is contemplated that any of the embodiments described herein may bemodified to include a plurality (e.g., two or more) diaphragms and/orpiezoelectric membranes to improve the sensitivity of the pressurereadings. For example, it may be desirable for the diaphragm(s) to havethe largest surface area possible. This may be accomplished through asingle, large diaphragm or a plurality of smaller diaphragms. It shouldalso be understood that the placement of the diaphragm and/orpiezoelectric membrane is not limited to the proximal end region of theLCP. In some cases, the diaphragm and/or piezoelectric membrane may bepositioned in or adjacent to a sidewall and/or near the distal endregion.

In some cases, the diaphragms and/or piezoelectric membranes may includecontours configured to increase the sensitivity and/or linearity of thediaphragms and/or piezoelectric membranes. Some illustrative contoursmay include, but are not limited to, a concave surface, a convexsurface, an undulating surface, a generally convex surface having agenerally concave central region, etc. It is contemplated that thecontours may be tuned for the application and/or placement of thedevice.

Regardless of the placement location of the LCP, some static pressuremay be applied to the diaphragm and/or piezoelectric membrane uponimplantation of the device. This may cause the diaphragm and/orpiezoelectric membrane to flex from its un-implanted configuration. TheLCP may be configured to detect changes in pressure over time which areindicated by a movement of the diaphragm. As such, and in some cases, itmay be desirable to pre-tune the diaphragm and/or piezoelectric membraneto optimize the pressure range of the diaphragm and/or piezoelectricmembrane when the LCP is implanted. This may be accomplished bydeforming the diaphragm and/or piezoelectric membrane during manufacturein a direction opposite to the static pressure exerted by the chamber ofthe heart such that the diaphragm and/or piezoelectric membrane are in aneutral configuration after implantation (as opposed to flexed inwardsunder the static pressure of the implantation chamber).

Those skilled in the art will recognize that the present disclosure maybe manifested in a variety of forms other than the specific examplesdescribed and contemplated herein. For instance, as described herein,various examples include one or more modules described as performingvarious functions. However, other examples may include additionalmodules that split the described functions up over more modules thanthat described herein. Additionally, other examples may consolidate thedescribed functions into fewer modules. Accordingly, departure in formand detail may be made without departing from the scope and spirit ofthe present disclosure as described in the appended claims.

What is claimed is:
 1. A leadless cardiac pacemaker (LCP) forimplantation in a ventricle of a heart, wherein the heart includes anatrium that contracts to supply blood to the ventricle, the LCPconfigured to sense cardiac activity and to deliver pacing therapy tothe ventricle of the heart, the LCP comprising: a housing; a firstelectrode secured relative to the housing and exposed to the environmentoutside of the housing; a second electrode secured relative to thehousing and exposed to the environment outside of the housing; apressure sensor housed by the housing, the pressure sensor is structuredto sense a change in pressure in the ventricle of the heart that iscaused by a contraction of the atrium of the heart, and in response,produce an electrical A-wave output signal; circuitry housed by thehousing and operatively coupled to the first electrode, the secondelectrode and the pressure sensor, the circuitry is configured todeliver a pacing therapy to the ventricle of the heart via the firstelectrode and the second electrode; the circuitry is further configuredto identify an atrial contraction of the heart based at least in part onthe electrical A-wave output signal from the pressure sensor; and thecircuitry is further configured to adapt a timing of delivery of atleast part of the pacing therapy delivered to the ventricle of the heartbased at least in part on the identified atrial contraction of theheart.
 2. The LCP of claim 1, wherein the pressure sensor comprises adiaphragm that is configured to move by an amount that is dependent onan applied input pressure, and wherein the pressure sensor produces anelectrical output signal that is dependent on the amount of movement ofthe diaphragm.
 3. The LCP of claim 2, wherein the circuitry isconfigured to determine one or more arrhythmias based at least in parton the electrical output signal produced by the pressure sensor.
 4. TheLCP of claim 2, wherein the circuitry is configured to monitor theelectrical output signal of the pressure sensor to identify aprogression of a chronic heart disease.
 5. The LCP of claim 2, furthercomprising communication circuitry configured to send information to aremote device that is based at least in part on the electrical outputsignal of the pressure sensor.
 6. The LCP of claim 2, wherein thepressure sensor further comprises a piezo material carried by thediaphragm that causes the electrical output signal of the pressuresensor to correspond to the amount of movement of the diaphragm.
 7. TheLCP of claim 2, wherein the housing comprises a thinned wall region thatforms at least part of the diaphragm.
 8. The LCP of claim 2, wherein thehousing defines a fluid cavity that is filled with an incompressiblefluid, and wherein the diaphragm is exposed to the incompressible fluidin the fluid cavity.
 9. The LCP of claim 1, wherein the pacing therapycomprises a Cardiac Resynchronization Therapy (CRT).
 10. The LCP ofclaim 1, wherein the pacing therapy comprises a Bradycardia Therapy. 11.The LCP of claim 1, wherein the pacing therapy comprises anAnti-Tachycardia Pacing (ATP) Therapy.
 12. The LCP of claim 1, furthercomprising a fixation member for fixing the housing to an implant sitein the ventricle of the heart.
 13. The LCP of claim 1, wherein thehousing includes an elongated body with a distal end and a proximal end,wherein the pressure sensor is exposed to the pressure in the ventricleof the heart at the proximal end of the housing.
 14. The LCP of claim 1,wherein the first electrode and the second electrode are each situatedalong an outer surface of the housing.
 15. A leadless cardiac pacemaker(LCP) for implantation in a ventricle of a patient's heart, wherein thepatient's heart includes an atrium that contracts to supply blood to theventricle, the LCP comprising: a housing; a first electrode securedrelative to the housing and exposed to the environment outside of thehousing; a second electrode secured relative to the housing and exposedto the environment outside of the housing; a pressure sensor configuredto produce an output signal that is responsive to a change in pressurein the ventricle of the patient's heart that is indicative of acontraction of the atrium of the patient's heart; and circuitry housedby the housing in operative communication with the first electrode, thesecond electrode and the pressure sensor, wherein the circuitry isconfigured to detect the change in pressure in the ventricle of thepatient's heart that is indicative of the contraction of the atrium ofthe patient's heart from the output signal of the pressure sensor, thecircuitry is further configured to deliver an electrostimulation therapyto the patient's heart via the first electrode and the second electrodethat is based, at least in part, on the detected change in pressure inthe ventricle of the patient's heart that is indicative of thecontraction of the atrium of the patient's heart.
 16. The LCP of claim15, wherein the pressure sensor includes a diaphragm that is structuredto be sensitive to the change in the pressure in the ventricle of thepatient's heart indicative of the contraction of the atrium of thepatient's heart.
 17. The LCP of claim 15, wherein the circuitry isconfigured to determine one or more arrhythmias based at least in parton the output signal produced by the pressure sensor.
 18. The LCP ofclaim 15, further comprising communication circuitry configured to sendinformation to a remote device that is based at least in part on theoutput signal of the pressure sensor.
 19. An Implantable Medical Device(IMD) for implantation in a ventricle of a heart, wherein the heartincludes an atrium that contracts to supply blood to the ventricle, theIMD comprising: a housing; a first electrode secured relative to thehousing and exposed to the environment outside of the housing; a secondelectrode secured relative to the housing and exposed to the environmentoutside of the housing; a pressure sensor housed by the housing, thepressure sensor is structured to sense a change in pressure in theventricle of the heart that is indicative of a contraction of the atriumof the heart, and in response, produce an output signal; controlcircuitry housed by the housing and operatively coupled to the firstelectrode, the second electrode and the pressure sensor, the controlcircuitry is configured to identify an atrial contraction of the heartbased at least in part on the output signal of the pressure sensor; andcommunication circuitry operatively coupled to the control circuitry,the communication circuitry configured to send information to a remotedevice that is based at least in part on the identified atrialcontraction of the heart.
 20. The IMD of claim 19, wherein the pressuresensor comprises a diaphragm that is configured to move by an amountthat is dependent on an applied input pressure, and wherein the outputsignal corresponds to the amount of movement of the diaphragm.